This invention relates to development systems for electrostatic processors and, more particularly, to
In a conventional electrostatic printing process of the type described in Carlson's U.S. Pat. No. 2,297,691 on "Electrophotography", a uniformly charged photoreceptor is selectively discharged in an image configuration to provide a latent electrostatic image which is then developed through the application of a finely divided, resinous material, called "toner". As is known, that process has enjoyed outstanding commercial success, especially in plain paper copiers and duplicators. Nevertheless, substantial effort and expense are still being devoted to the perfection of the process, including the development step.
The vehicle normally used in electrostatic processors to deliver the toner is a multi-component developer comprising toner particles and relatively coarse "carrier" particles. The toner and carrier (or sometimes carrier coating) components are formed from materials which are removed from each other in the triboelectric series, thereby enabling a triboelectric charging process to be employed to induce electrical charges of opposite polarities on the toner and carrier particles. Furthermore, triboelectric ranking is taken into account while selecting the materials for those components to the end that the polarity of the charge imparted to the toner particles opposes the charge of the latent image. Thus, in operation, there are competing electrostatic forces acting on the toner particles. Specifically, those particles are initially attracted to carrier particles, but some toner is subject to being electrostatically stripped from the carrier whenever developer is brought into the immediate proximity of or actual contact with an image bearing photoconductor.
Experience has demonstrated that the useful life of a developer charge can be prolonged by adding additional toner to the developer from time-to-time. The additional toner is, of course, needed to maintain the toner concentration of the developer at a suitably high level inasmuch as toner is consumed in the development process. Hence, most development systems include a toner dispenser.
Briefly, a toner dispenser normally includes a reservoir for storing a supply of toner, together with means for feeding toner from the reservoir to, say, the sump of a development system. Some toner dispensers are more or less permanent fixtures, but there is a trend toward removable types. It has, in short, been recognized that in situ loading of a toner dispenser is not particularly desirable because of the risk that the processor will be contaminated by toner accidentally spilled during the loading of the reservoir. However, the pre-loaded, removably mounted toner dispensers previously proposed have not been altogether satisfactory. Most of them are relatively expensive units, and some are difficult to mount and remove.